vw manual transmission on 1990 Volkswagen Cabriolet

I have a 1985 vw Cabriolet w/ manual transmition. There is a round rubber seal with a hole in it on top of the bell housing. Does this opening stay open, or should it be plugged?

Asked by for the 1990 Volkswagen Cabriolet
It is a plug that allows ignition timing to be checked using a timing light. It does not seal any fluids but does prevent anything falling into the bell housing, and prevents injury when working on the engine with the engine running.
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i think they had a recall on that year here in california because the transmissions wold not shift out of reverse or go into 1st.that was about 8mos ago,i dont know if you are aware of it,if not i hope i helped you